Motor control apparatus



March 11, 1941. MacKAY HOTOR CONTROL APPARATUS filed April 17, C

INVENT R.

BY ii CMPFM I/vu ATTORNEYS Patented Mar. 11, 1941.

UNITED STATES PATENT OFFICE Wallace &

Tiernan Products, Inc., Belleville,

N. J., a corporation of New Jersey Application April 17, 1936, Serial No. 74,895

1 Claim.

This invention relates to systems for indicating, repeating, or reproducing, movements of an object, usually at a distance. cific aspect, it relates to telemetric systems.

Oneof the objects of the invention is to provide a system of the class described which is both sensitive and powerful. Other objects and advantages will appear upon reading the following written description of what I now consider to be a preferred form of my invention and the principle thereof, and the best mode in which I have contemplated applying that principle.

*In Fig. 1 of the drawing I have illustrated, somewhat diagrammatically, what I now consider a preferred embodiment of my invention.

Fig. 2 is a fragmentary diagrammatic view showing a modified form of connections.

While my invention is applicable in other environments and for other purposes wlt-hin the 2 scope of the appended claim, it will be assumed that it is to be applied to the indication (at ill) of the positions of a float ll, i. e. the level of aliquid, at a remote point.

The particular form of invention illustrated in 25 Fig. 1 comprises a group of instrumentalities for producing a controlling E. M. F. in accordance with movement of the object whose position is to be indicated or repeated, in the particular case,

a float; a group of instrumentali-ties for producing current variations under the control of the controlling E. M. F.; and a translating device under control of the current variations for actuating the indicator or repeating instrument. While other forms of instrumentalities may be 5 employed for producing the controlling E. M. F., such, for example, as a resistance bridge or a capacity bridge, I have shown an inductance type of bridge which I shall now proceed to describe. The inductance bridge illustrated comprises 40 two identical stationary inductance coils l2, I3 having vertically movable cores l4, l5 of magnetizable metal. The outer ends of the coils I2 and I3 are connected by conductors a suitable source of E. M. R, such as the sec- 45 ondary winding l8 of a transformer I9, is connected between center taps of the coils l2 and I3. The primary winding of the transformer I9 is supplied with A. C. from any suitable source, such, for example as a 110 volt 60 cycle line.

50 When the bridge is balanced, dependent upon the relative positions of thefcores l4 and I5, there will be no difference of potential between the conductors Iii-I1, produced by the source l8. If, however, the core H moves 'up or down with respect to the core I! the bridge wm be unbal- From a more spe-.

I6, 11, and

(Cl. 172-239) anced and there will be a difference of potential produced by the source 18 across the conductors l6-I'l of a relative polarity dependent upon the direction of movement of the core l4. By causing the core I i also to be moved vertil cally in the proper direction, the balance may be restored and there will then be no difference of potential between the conductors Iii-I1, produced by the source I 8.

The core I is shown connected, as indicated 10 by dotted lines, to a float ll whose rise and fall in response to liquid level causes the core correspondingly to be raised or lowered.

The core I5 is shown connected, as indicated by dot and dash lines, to the rotor 22 of a translating device (motor 23) which rotor is shown connected also to the pointer of the indicator I0. These connections, indicated by the dot and dash lines, may assume the form of the connections between the core 9a, pointer 1a, and rotor I 9, 20 shown at the left hand side of Fig. 1 of Letters Patent of the United States No. 642,662, patente February 6, 1900, A. U. Alcock.

The rotor 22 is so controlled by an unbalance of the above described inductance bridge as to 25 cause the balance to be restored by movement of the core IS. The manner in which this control is effected, and the combination of instrumen'talities whereby it is effected, are, however, essentially different from those disclosed in the cited prior patent and essentially different from any prior art of which Iv am aware.

The conductors'i6 l1 of the bridge are shown connected to the input of an amplifier 2| whose output is connected to a transformer for control ling the motor 23 (hereinafter described). While amplifiers of more or less stages and of dilferent types may be employed, I have illustrated a some what standard type of amplifier comprising two tubes and known as a class A amplifier. 40

The conductors l6 and I! are shown connected respectively to the control grid and cathode of a vacuum tube 24. A satisfactory form of such tube is known in the art as RCA-57.

The plate or output circuit of the last stage vacuum tube 21 contains the primary winding 26 of the transformer 25. A satisfactory form of such tube 21 is known in the art as RCA-2A3. The other connections of the amplifier 2! will be understood by those skilled in the art who are familiar with .the symbols employed in the drawing and especially in view of the following description.

The amplifier is connected as shown, the filament transformer and filament-energizing cirthe secondary winding cults of the tubes being omitted for clarity in illustration. The usual and well known coupling resistances, biasing resistance, blocking and bypass condensers, etc., are employed. The plate circuits of the tubes 24, 21 are supplied with direct current from the full wave rectifier 28 (which may be a RCA- tube) through the lilter 23; the filament of the tube 28 being energized by the secondary winding 30 of the transformer l9 and .the plates being connected across the transformer secondary winding 3|, whose mid-tap is connected to the conductor l1.

The secondary winding 32 of the transformer is connected to the translating device (motor) 23 in a manner presently to be described.

The motor 23 is a motor known in the art as a shading coil induction motor. It comprises the rotor 22 of the squirrel cage type, and a stator 33 (shown in dotted lines) having a main winding 34, and four shading coils 35, 36, 31 and 38. A motor of this general type and construction is disclosed at 252627-28--29-30-31 in Letters Patent of the United States No. 1,895,880, patented January 31, 1933, P. W. Cummings, and also at A-E-5-X-XY--Y in Letters Patent of the United States No. 2,007,240, patented July 9, 1935, D. N. Crosthwait Jr.; but my motor 23 is so designed, constructed, and controlled that it is essentially difi'erent from those of the prior art and also efiects improved results.

The number of. turns of each of the four shading coils 35-36-31-38 is the same as the number of turns of any of the others of the said four shading coils; but the shading coils are so wound and/or connected that, even with the main winding 34 energized, no current flows through any of the shading coils unless an E. M. F. is induced in 32 by the primary winding 26 of the transformer 25. The four shading coils 35-33-31--38 are shown connected in series with each other and in series with the seccndary winding 32. When the main winding 33 is energized there is an E. M. F. induced thereby in each of the four shading coils, but the sum of these so-induced E. M. F.s is zero in the series circuit and they produce no current flow therein.

As a consequence, when the bridge i2-i3 is in balance, i. e. when the entire system is in normal position, no current flows through any of the shading coils.

The reason no current flows in the series circuit 32-35-3G-31--38 when no E. M. F. is induced in the secondary 32 by the primary 26, is that the E. M. F.s induced in the coils 38, 31 by the winding 33 tend to cause current to flow in one direction in the series circuit whereas the E. M. F.s induced in the coils 36, 35 by the winding 34 tend to cause current to flow in the op posite direction in the series circuit, so that the net result is no flow of current.

However, when an E. M. F. is induced in the secondary winding 32 by change in current in the primary 26, current flows in the shading coil circuit and the coils 35-36 produce a rotative effect upon the rotor 22 in one direction and the coils 31'-3B produce a rotative effect upon the rotor 22 in that same direction; i. e. all of the shading coils produce a rotative efiect in the same single direction. The E. M. F. induced (by the primary 26) in the secondary 32 adds to the E. M. F.s induced (by the winding 33) in the coils 35, 36 (or 31, 38) and opposes and preferably exceeds the E. M. F.s simultaneously induced (by the winding 34) in the other coils 31,

' flowing through the main produce rotation of the rotor.

38 (or 35, 36) Of course, whenever current in the circuit 32-35-3331-38,-the current is the same in all of the coils, the circuit being a series circuit.

The direction in which the rotor turns when current is supplied to the shading coils from the secondary 32, depends upon the relative direction or phasing of such current with respect to that winding 34. It will benoted that the main winding 33 is connected to the line to which the primary 20 of the trans- .former I9 is connected.

In arrangements such as that disclosed in the cited Patent'No. 1,895,880, only two of the four shading coils are utilized at a time in producing rotor torque or turning effort, the other two being idle. In arrangements such as those disclosed in the cited Patent No. 2,007,240, the turning efiort produced by two of the four shading coils is always opposed by the turning efiort produced by the other two shading coils and an unbalance or differential action is relied upon to But, as stated, in my motor 23, all four of the shading coils are simultaneously utilized to produce torque in the same direction and the action is cumulative and not differential.

The system shown in signed and adjusted so as Assume that the primary I9 is connected to the the filaments of the Fig. 1 is constructed, de-

to operate as follows. 20 of the transformer tubes 24 and 21 are being supplied with current through the usual filament current supply apparatus (not shown), and that the parts are in the position shown in the draw; ing with the bridge l2-l3 in balance. N0 E. M. F. is induced in the secondary winding 32 of the transformer 25, no current flows in the shading coil circuit 32-35--36-31'-38, and the rotor 22 remains stationary.

Assume now that the float ll moves the core 54 up or down, in response to a rise or fall of the liquid whose level is to be indicated. The resultant unbalance of a properly phased voltage on the control grid of the voltage amplifier tube 24 (dependent upon the direction of movement of the core M) and, in the amplifier 2| 0'. the type disclosed (a class A amplifier), this causes a decrease or increase in the plate current' of the tube 21. This change in current flowing through the primary winding 26 induces an E. M. F. in the secondary winding 32 and causes the rotor 22 to turn in such direction as to move the core IS in such direction asto restore the balance of the bridge I2-l3. If

the core It was moved upwardly by the float H,

the core IE will be automatically moved upwardly by the rotor 22, and downward movement of the core M will result in downward movement of the core I5. When the core l5 has thus been automatically moved by the rotor 22 so as to restore the balance of the controlling bridge circuit l2-l3, there is no longer any change in current in the primary winding 26 and the rotor 22 quickly comes to restby an electric braking action.

Thus the core i5 is automatically caused to repeat any and all movements of the core 14 and the indicator I0 may be calibrated so as to indicate the level of the liquid upon which the float ll rests. The inductance coil l3 and the indicator l0 and associated apparatus may be remotely located with respect to the float il and coil l2. 7

My system is sensitive and powerful and sub-v the bridge l2--l3 impresses 4 volt 60 cycle line, that v i. e. quickness in response,

. at the rotor 22.

"1,135 of shading stantially dead beat. In an actual system constructed as shown and above described, except that a resistance bridge was utilized instead of the inductance bridge illustrated, I have found that even very rapid movements of one of the slides of the control bridge are, faithfully and rapidly repeated by the other and rotor-driven slide of the bridge and the torque of the rotor is 'so powerful as to be more than that required to operate a recorder to which the rotor was also mechanically coupled. Moreover, there is 'no hunting and the rotor is quite dead beat in its operation. Quite minute changes in thevoltage applied to the control grid of the tube 24 produce large changes in the current in the primary winding of the step-down transformer 25 and sensitive and comparatively powerful response by the rotor 22. My invention is therefore not only applicable to indication of liquid level, where considerable lag between float movement and indicator movementis permissibl, but it is admirably adapted for use in telemetric and other systems in which great sensitivity, is required. Withal my system is one which provides ample power Besides other changes which may be made in the particular system disclosed, withoutdeparting from the scope of at least some of the appended claims, I have shown, in Fig. 2, a dinerent way of energizing the shading coils, which may be employed in some cases.

In Fig. 2, the parts I22, I33, I34, I35, I35, I31 and I33 correspond generally to the parts 22, 33, 34, 35, 35, 31 and 33, respectively of Fig. 1. Instead-of employing one step-down transformer 25, two step-down transformers I25, 225 are employed and their primary windings I25, 225 are connected-in series in the plate ,on output circuit of the tube 21. The secondary winding I32 of the transformer I25 is connected in series with the shading coils I31, I35 and the secondary winding 232 of the transformer 225 in the primaries I25, 225, the pair of coils I35, I35

tend to rotate the rotor I22 in one direction and the pair of coils. I31, I35

being equal but opposite. E. M. F. is induced in the secondaries I32, 232 by a change in current in the primaries I25, 225, the current'in one set I35, I35 (or I31, I35) of shading coils is increased and the current in the (or I35, I35) of shading coils However, when an set I35, I35.oi shading coils is in the same direction as the torque produced by the other set coils. The direction of this is connected in series with the shading coils I35, I35. The

tend to rotate the ro- ,to'r in the opposite direction; these two torques combined torque depends upon the phasing of the varying current in the output circuit of the amplifier with respect to that in the main winding I34. The above described reversal of current is attained by causing the E. M. F. supplied by one of the secondaries (I32, 232) not only to oppose but to exceed the sum of the E. M. F.s induced (by the winding I34) in the set of shading coils .connected in series with that particular secondary.

It will be understoodthat the remaining connections not shown in Fig. 2 may be the same as shown in Fig. 1.

As disclosed above, the rotor 22 of the motor 23 is of the squirrel cage type. While other types of rotors, such as, for example, those of the hysteresis or remanence types, with properly designed shading coils, may be employed in certain circumstances and conditions of use, I have found the particular type described above to be satisfactory and I now prefer that type, particularly when comparatively large torque is desired. 7

In accordance with the provisions of the patent statutes, I have herein described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiments thereof, but I desire to have it understood that the apparatus disclosed is only illustrative and that the invention can be carried out by othermeans. Also, while it is designed to use the various features and elements in the combinations and relations described, some of these may be altered and others omitted and some of the features of each modification may be embodied in the others without interfering with the more general results outlined, and the invention extends to such use the-rotor in the other direction, a control ole ment, a second control element remotely located therefrom, means comprising a normally balanced electrical circuit extending from one of said control elements to the other, means responsive to unbalance 01' said circuit for operating said first control element to restore said balance, said last mentioned means including means for reversing the current in either of said sets of shading coils with respect to the current in the other of said sets of shading coils to cause rotation of the rotor in either desired direction, and means automatically adjusted by the resulting rotation of the mal -relative flow of current in said shadin coils, when said balance is restored.

JOHN R. MAOKAY.

rotor for restoring the nor- 

